Both serotonergic and dopaminergic neurons exert releasing and inhibiting influences on pituitary prolactin secretion. Recent studies suggest that opiate receptors may affect these aminergic neuronal networks and their influence on prolactin release. Our studies will address the neuroanatomical regions of the hypothalamus and extrahypothalamic pathways that may be operative in opioid or aminergic influences. We propose to use electrical stimulation of discrete neural regions, agonists and antagonists of aminergic compounds, and naloxone, and opiate receptor blocker, to find out more about the neural mechanisms that influence prolactin release. We will monitor serum prolactin changes in rhesus macaques after various treatments known to block or facilitate prolactin release. Ovarian estradiol also modulates pituitary prolactin secretion, and we will investigate the influence of this steriod on the aminergic and peptinergic neuronal systems. The patterns of prolactin secretion in humans and rhesus macaques are similar during a 24-hour period; increased levels occur during the nighttime. Destruction of various neural areas that influence this circadian rhythm of prolactin secretion will be evaluated with the rhesus macaque as a model. We hope that these studies will provide insights into the neurological mechanisms that influence prolactin secretion and the role of prolactin in normal reproductive function.